Iruka's parents were killed in the Nine-Tails' Attack on Konoha twelve years before the beginning of the series. Initially, a young Iruka was present on the battlefield, and wanted to stay in order to protect his mother. His father declared that it was the parents' duty to keep their child safe from harm. He was forcibly removed from the battlefield by an unknown shinobi.

With his family gone, Iruka had no one to give him attention. Iruka thereafter became a prankster much like Naruto would later become, trying to gain attention to stave off his loneliness. He would spend his time at the monument where his parents' names were engraved, and, in his darkest moments would be cheered up by the Third Hokage. Mizuki was a childhood friend of Iruka's after the Nine-Tails Attack, and usually made him feel better. In the anime, it was noted that due to other people giving Iruka more attention than they do to Mizuki, Mizuki's kindness to Iruka revealed to be an act just to gain the Hokage's approval, all the while making Iruka miserable discreetly.

In the anime, it was revealed that Iruka became a teacher because he wanted to pass on the Will of Fire to the next generation in this manner, inspired by the Third Hokage's wisdom. When Naruto became his student, he found it awkward to deal with the person containing the very monster responsible for his parents' death. He tried to ask the Third Hokage if he could not teach Naruto, though he was eventually disabused by the notion by Kakashi Hatake. Later, Naruto went into the woods to steal items from corpses. Iruka chased him down and protected him from Takigakure spies who were attacking Naruto, eventually backed up by Kakashi. After saving Naruto and bringing back the document attached to the artifact the latter retrieved, he thanked the Third for assigning Naruto to him. He thus resolved to be straight forward and deal with Naruto strictly in class from then on, in order to train him to become a fine shinobi.

Iruka is a man of average height and build. He has black hair that he keeps in a ponytail, dark eyes and a scar that runs across the bridge of his nose - which he has had since his youth. He wears the standard Konoha shinobi outfit complete with forehead protector, sandals, and flak jacket. His sleeves are also rolled up about ¼ way. As a child he wore a simple outfit along with mesh-armour underneath it.

Iruka is described as being both big-hearted, and soft-hearted. This is most often seen through his teaching methods, often giving a watchful eye over his students as they progress. This however, does not mean that he is a pushover, as he can be stern when the situation calls for it most often seen when he shouts at his students in order to get them to obey him. Despite the tragedy of losing his parents at a young age, Iruka remained a determined and strong-willed individual with a kind disposition. This is seen from his lack of hostility towards Naruto Uzumaki who was often the victim of misplaced anger at the Nine-Tailed Demon Fox who was sealed within Naruto.

As a child growing up without his parents, Iruka turned to performing antics in the Academy in order to gain recognition from others who would otherwise pass him over or look at him with pity for being an orphan. This allowed him to also see some of these signs and understand what they meant when displayed by Naruto. Due to Iruka's more nurturing and compassionate nature, Naruto views him as a mentor and Iruka in turn, views Naruto as a younger brother. The two enjoy their favourite ramen dish at Ramen Ichiraku whenever Naruto returns from a mission, where Iruka gets an opportunity to see how Naruto is developing as a ninja. Iruka's refusal to allow Naruto to graduate at first was not out of spite, but merely out of caring strictness and a desire for Naruto to work harder and reach his own potential.

He also has a great sense of duty, honour and selflessness as seen when he protected Naruto from Mizuki's attack, suffering a shuriken wound in his back in order to protect him. He greatly admires both the Third Hokage who was there to help him during his troubled period as a child and believes strongly in the Will of Fire of the village. As a result, he regards the children of the village as the backbone of Konoha - even being willing to sacrifice his own life to ensure their safety.

As a head instructor of the Academy, he is clearly proficient in all forms of basic ninja skills. He has some ability with Barrier Ninjutsu, as he is seen creating a barrier in an attempt to restrain Naruto. Iruka is also very perceptive as he is able to assess situations carefully and quickly while under threat.

In the anime, Iruka's skills were expanded upon and it was shown that he had some knowledge of genjutsu, as demonstrated when he posed as an enemy Amegakure ninja to test Sakura, and he also saw through the genjutsu cast by Mizuki. During the Mizuki Strikes Back Arc, Iruka showed some skill in taijutsu as well, by keeping on equal footing with the now-improved Mizuki in his attacks. Iruka was also shown using Sealed Bomb Square Release, which consists of setting an array of exploding tags and, once the target has entered the area, setting the tags to detonate if the target moves.

Also, in the anime, Iruka displayed what seems to be an echolocation ability where he can get a sonar image of his surrounding area, perhaps playing on the meaning of his name, "dolphin". [source: wikia]